Dengue virus (DENV) causes the most prevalent mosquito-borne viral disease: over 2.5 billion people are at risk for infection in over 100 countries. Each year, dengue virus infects and exhibits symptoms in about 100 million people worldwide. Of those infected, about 250,000-500,000 develop severe illness, and up to 50,000 die from dengue hemorrhagic fever (DHF) each year (see, e.g., Dengue and dengue hemorrhagic fever, World Health Organization Media center, Fact Sheet No. 117, March 2009; Deen J L et al., 2006, Lancet 368, 170-173; Kyle J L et al., 2008, Annu Rev Microbiol 62, 71-92). In 2010, dengue virus re-entered the US via the Florida Keys, after an absence of sixty-five years (see, e.g., Homeland Security News Wire, 2 Jun. 2010).
There are four closely related, but antigenically distinct, dengue virus serotypes, namely DENV serotype 1 (DENV-1), DENV serotype 2 (DENV-2), DENV serotype 3(DENV-3), and DENV serotype 4 (DENV-4). Each serotype comprises several genotypes that exhibit differences in their infection characteristics in both the mosquito vector and the human host. Recovery from infection by one serotype provides lifelong immunity against that serotype, but confers only partial and transient protection against subsequent infection by other serotypes. One of the confounding problems that has faced vaccine development for decades has been this inability of one serotype to protect against infection by another. Rather, the induced humoral immune response to one DENV serotype as a result of infection can enhance the infection and disease processes brought about by a subsequent infection with another DENV serotype. Such subsequent infection is thought to increase the risk of developing dengue hemorrhagic fever (DHV), a potentially lethal condition. (see, e.g., WHO Fact Sheet No. 117, ibid.; Halstead S B et al., 2007, Lancet 370, 1644-1652; Dejnirattisai W, et al., 2010, Science 328, 745-748.)
Dengue virus is a single positive-stranded RNA virus of the Flaviviridae, genus Flavivirus. The viral genome of about 10.7 kilobases is translated as a single polypeptide that is cleaved into three structural proteins (namely a capsid protein (C), a membrane protein (M, prM/M), and an envelope protein (E)), and seven non-structural proteins (namely NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5).
The initial step of dengue virus infection is entry of the virus into cells; such entry is mediated by DENV envelope E, a glycoprotein (see, e.g., Dimitrov D S, 2004, Nat. Rev. Microbiol. 2, 109-122). DENV E is a type II fusion protein and consists of three domains (see, e.g., Dimitrov D S, ibid.; Kuhn R J et al., 2002, Cell 108, 717-725). The domains are named ED1, ED2, and ED3, respectively; other names for the envelope domains are domain I (DI), domain II (DII), and domain III (DIII, or Env-DIII), respectively. ED3 has been proposed to contain a receptor binding domain (Huerta V et al., 2008, Virus Res 137, 225-234; Crill W D et al., 2001, J Virol 75, 7769-7773).
Antibodies are important for protective and pathogenic immune responses to dengue virus (see, e.g., Halstead et al., ibid.). Their major target is the DENV E protein (see, e.g., Marasco W A et al., 2007, Nat Biotechnol 25, 1421-1434; Modis Y et al., 2005, J Virol 79, 1223-1231; Roehrig J T et al., 1998, Virology 246, 317-328; Bedouelle H et al., 2006, FEBS J 273, 34-46; Thullier P et al., 2001, J Gen Virol 82, 1885-1892). The amino acid sequences of E proteins for DENV-1, DENV-2, DENV-3, and DENV-4 differ by 25% to 40%; the amino acid sequences of E proteins for genotypes within a DENV serotype vary by up to 3% (see, e.g., Holmes E C et al., 2003, Infect Genet Evol 3, 19-28). Antibodies against ED3 are both serotype specific and cross-reactive; such antibodies are effective DENV neutralizers, typically better than antibodies against ED1 or ED2 (see, e.g., de Alwis R, et al., 2011, PLoS Negl Trop Dis 5, e1188; Balsitis S J, et al., 2010, PLoS Pathog 6, e1000790; Beltramello M et al., 2010, Cell Host Microbe 8, 271-283; Sukupolvi-Petty S et al., 2010, J Virol 84, 9227-9239; Shrestha B et al., 2010, PLoS Pathog 6, e1000823; Rajamanonmani R et al., 2009, J Gen Virol 90, 799-809; Sukupolvi-Petty S et al., 2007, J Virol 81, 12816-12826; Gromowski G D et al., 2010, Virology 407, 237-246; Matsui K et al., 2010, J Gen Virol 91, 2249-2253; Matsui K et al., 2009, Virology 384, 16-20; Gromowski G D et al., 2008, J Virol 82, 8828-8837; Gromowski G D et al., 2007, Virology 366, 349-360; Hiramatsu K et al., 1996, Virology 224, 437-445; Lok S M et al., 2008, Nat Struct Mol Biol 15, 312-317). The cross-reactive antibodies are generally weaker neutralizers than the serotype-specific antibodies (see, e.g., Sukupolvi-Petty S et al, 2007, ibid.; Gromowski G D et al., 2008, ibid.). Anti-ED3 serotype-specific and cross-reactive antibodies are elicited using ED3 as a vaccine immunogen (see, e.g., Guzman M G et al., 2010, Vaccines 9, 137-147; Bernardo L et al., 2011, Vaccine 29, 4256-4263; Bernardo L et al., 2009, Clin Vaccine Immunol 16, 1829-1831; Izquierdo A et al., 2008, Virus Res 138, 135-138; Simmons M et al., 1998, Am J Trop Med Hyg 58, 655-662; Simmons M et al., 2001, Am J Trop Med Hyg 65, 159-161; Srivastava A K et al., 1995, Vaccine 13, 1251-1258) and in infected humans (see, e.g., de Alwis R et al., ibid.; Midgley C M, 2011, J. Virol. 85, 410-421; Rothman A L, 2004, J. Clin. Invest. 113, 946-951; Wahala, W M et al., 2009, Virology 392, 103-113). Recently, several human monoclonal antibodies were selected from immortalized B cells obtained from DENV-infected people, a few of which also exhibited some cross-reactive neutralizing activity against all four serotypes; a cocktail of three of antibodies targeting distinct epitopes and engineered to prevent FcγR binding was successful in a mouse model of disease when administered one day after challenge (Beltramello M et al, 2010, ibid.).
There remains a need for an effective therapeutic, an effective prophylactic, or an effective therapeutic and prophylactic against dengue virus infection, not only to protect an individual from an initial infection, but also to protect that individual from subsequent infection not only by the same DENV serotype but also by any and all other DENV serotypes. As such, there is a need for an anti-DENV antibody that cross-reacts with and neutralizes DENV-1, DENV-2, DENV-3, and DENV-4 dengue virus serotypes. There is also a need for a vaccine that comprises an epitope recognized by such a cross-reactive anti-DENV antibody to protect an individual from dengue virus infection.